The invention pertains to a dedicated display device comprising means of detection of proximity. Such devices are used in particular for the construction of communication terminals of the type allowing an operator to transmit and to receive information within the framework of a friendly exchange with a processor. The invention finds a particular application in respect of the screens of interactive terminals comprising dedicated liquid crystal screens. The expression dedicated screen is understood to mean a screen comprising at least one or more pictograms locked-in during the design of the screen.
Such screens comprise two plates at least one of which is transparent. Between these plates are disposed liquid crystal molecules. To excite the liquid crystal molecules and to modify the polarity of a light ray which passes through them, the screen comprises transparent electrodes situated on internal faces of the two plates. In dedicated screens, in order to simplify the routing of connection pads of the electrodes, it is known to embody the electrodes of each plate in such a way that the whole set of pictograms is situated in an identical manner on the two electrodes opposite one another.
Dedicated screens are customarily rendered touch-sensitive by disposing one or more transparent touch layers on the device, these being based on contact or on capacitive or inductive effect or the like. The device can then serve to delimit pressing zones of this layer according to a desired composition. The pressing of the layer is usually done by a finger of an operator. The drawbacks associated with these known methods relate to the cost of the responsive component added to the screen and to the fact that the visual information provided by the device is inevitably altered by the add-on touch layers.
It is moreover known from patent FR 88 05665 to embody a display with incorporated touch-sensitive surface wherein one of the electrodes called the counter-electrode is used as responsive element, this counter-electrode possibly being split up into a plurality of zones each constituting a counter-electrode.
The application of the known principle to dedicated displays has a certain number of drawbacks in that it does not make it possible to simply adapt the size of the counter-electrodes to the various shapes and number of dedicated pictograms associated with a touch-sensitive zone. Thus the routing of the feed pads of each touch-sensitive counter-electrode may be rendered very tricky on account of the numerous feed pads of said associated pictograms opposite this same responsive counter-electrode.
Moreover, in a dedicated display, it is not possible to ignore the influence of the individual surface of each pictogram as regards the responsive counter-electrode since the designer of the pictogram is entirely at liberty to make it as small or as large as he so wishes for his application.
Thus, in the known art this would lead to the defining of a counter-electrode that is unsuited to the requirement of detection by capacitive effect on account of its overly small size and/or by parasitic images which are at risk of being engendered by the connection pads.
The invention aims to alleviate these problems by proposing a touch-sensitive dedicated screen with no added touch-sensitive layer.